The protection and tracking of a tangible medium containing data, such as a confidential paper, has recently become both more important and less successful. This is because a tangible medium, such as papers, is typically very easy to hide and remove from otherwise secure facilities. Further, the copying of a tangible medium has become easier with the advent of more sophisticated copying devices. When copies have been made, it is often difficult to determine what is an original and what is a copy. Further, it is often difficult to determine where the copy originated.